Stencil-forming sheet material assembly



Sept. 1964 1'. ca. WARTMAN ETAL 3,

STENCIL-FORMING sum MATERIALASSEIMBLY Filed May 12, 1961 g 72 Wrzwrozs ZT OMAJ 6. WARrMA/v GER/MRO 144A. R/[RCK/MUER United States Patent G 3,149,563 STENClL-FORMHNG SHEET MATERIAL ASSEMBLY Thomas G. Wartman, Mendota Heights, and Gerhard W.

R. Puerclrhauer, Maplewood, Minn, assignors to Minnesota Mining and Manufacturing Company, St. Paul,

Minn., a corporation of Delaware Filed May 12, 1961, Ser. No. 109,761 12 Claims. (Cl. 101-125) This invention relates to graphic duplication methods involving the application of heat energy and to sheet materials useful therein. One particularly important aspect of the invention involves the preparation by thermographic copying methods of novel stencil-like intermediates from which multiple copies may be produced by simple heating of the intermediate in contact with a suitable receptor sheet.

In a typical example, a heat-sensitive sheet material as hereinafter described is placed in heat-conductive contact with a differentially radiation-absorptive graphic original which is then briefly exposed, through the sheet material, to intense radiation to provide a heat-pattern which produces in the contacting sheet material a corresponding stencil pattern. The sheet material is then placed in contact with a suitable receptor sheet and is briefly heated, for example in an ironing-machine. A duplicate copy of the original is produced on the sheet material. Additional copies are produced on repeating this step of the process with additional receptor sheets.

In the drawing,

FIGURE 1 illustrates the irradiation of a graphic original 10 through a sheet material 11, comprising inner film 12, central layer 13, and outer film 14, with radiation 15 to provide a stencil-like pattern 16 in film 12 corresponding to the radiation-absorptive image area 17;

FIGURE 2 illustrates the transfer of image-forming material from the central layer 13 through the pattern 16 in the film 12 under the influence of heat applied as indicated by wavy arrows 20, to form on the receptor sheet 18 a visible duplicate 19 of the original image area 17;

FIGURE 3 illustrates another means of obtaining an image in which a receptor sheet 30 previously moistened with a thin surface coating of a suitable solvent 31 is first pressed against the pattern inner film 12 of the sheet material 11 to cause solution and transfer of imageforming material from the central layer 13 through the pattern 16, forming a visible duplicate 32 of the image area;

FIGURE 4 illustrates still another method of copying in which a sheet material 40, in this case consisting of fibrous support layer 42 and thin film layer 41, previously subjected to a heat-pattern as in FIGURE 1 to provide pattern areas 46, is placed in contact with a visibly heatsensitive copy-sheet 48 which is partially radiation-absorptive, and the composite is briefly subjected to intense radiation 45, producing visible image areas 47 in the heatsensitive copy-sheet;

FIGURE is a schematic illustration of method and apparatus typically used in making a sheet material as employed in FIGURES 1-4; and

FIGURE 6 illustrates a further and preferred form of sheet material 71 having a thin outer film 74, a central layer 73, a thin inner film 72, and an extremely thin surface lubricant or parting layer 75.

The stencil-forming sheet material of the present invention will be seen to provide a number of advantages. The form illustrated in FIGURES 1-3 may contain any of a wide variety of image-forming components within the central layer 13, the same being fully covered and protected by the surface film layers 12 and 14. Contact of ice the image-forming components with other surfaces, for example with paper originals or receptors or with the hands of an operator, is avoided. Loss of liquid or volatile materials is prevented. The sheet material serves as a reservoir of image-forming material so that large numbers of copies may be made.

The copying procedures illustrated in FIGURES 1-3 involve the formation of a heat-pattern at the radiationabsorptive image area 17, resulting in the formation of numerous tiny channels or apertures through the areas of the thin film 12 associated therewith. Liquid, volatile, soluble or fusible image-forming materials contained in the central layer 13 and between the films 12 and 14 are then transferred from the intermediate through the perforate image areas 16 to suitable receptor sheets for formation of the desired image. As the image-forming material is depleted from the space immediately above the channeled area 16, more is continuously supplied from adjacent areas of the central layer 13.

The image-forming material may for example be in the form of colored fusible solids such as waxes containing dyes or pigments, colored liquids such as viscous inks, volatile coloring agents such as volatile organic dyes, and colored or colorless transferable reactant materials capable of undergoing a color-forming reaction with co-reactant materials present in the receptor sheet. Colorless or slightly colored materials which may subsequently be converted to strongly colored form or, being ink-receptive, may subsequently be selectively coated with liquid or powdered inks or other coloring agents, may likewise be employed as image-forming components in the central layer 13 of the sheet materials of this invention.

The image-forming components are retained within the fibrous central layer of the sheet material both for convenience in assembling the several layers and, particularly in the case of normally liquid or low-melting solid materials, as a means of maintaining such materials in position within the. assembly. Thin porous paper is conveniently used for this purpose, but other thin absorbent webs are equally satisfactory. They may be fastened to the surf-ace films by means of direct fusion or embedding, or by means of adhesive coatings which may additionally serve to reinforce or unify or otherwise strengthen the absorbent web. The adhesive coating in the absence of a fibrous or absorbent web may itself be sufficiently porous to permit transfer of image-forming components.

The thin inner film 12 of FIGURES 1-3 retracts or shrinks to a lace-like porous or perforate structure when heated to temperatures available in the thermocopying process described, and which may be in the neighborhood of -250 C. Thermoplastic oriented or tens-ilized polymeric films of minimum thickness are preferred. The

same film may be used as the permanently impermeable continuous outer film 14, since the heat produced at the irradiated image of the original is ordinarily dissipated sufficiently within the sheet material to avoid softening, re

traction and perforation of the outer film. Thicker films are more easily handled, however, and are preferred for the outer layer It will be appreciated that all of the components of the sheet material must be so selected and associated as to produce a structure which is transmissive of the radiant energy employed when providing a heat-pattern in accordance with the process indicated in FIGURE 1. Radiations rich in infra-red are ordinarily employed in these thermographic front-printing processes, and components have previously been described which are sufficiently non-absorptive of infra-red radiation to be successfully used in these novel sheet structures. On the other hand, heat-patterns otherwise obtained are also effective in forming the porous image areas 16. For example, brief contact with heated metal type faces, particularly through a thin intervening silk screen or superficial surface coating of protective lubricant, produces a corresponding porous image pattern in the thin film 12; and other ways of applying an effective heat-pattern are known. For such procedures, the sheet material need not be radiation-transmissive.

The sheet material 40 of FIGURE 4 includes neither an outer film layer nor an image-forming component, but instead consists only of a thin tensilized plastic film 41 and a fibrous Web 42. Surprisingly, this form of sheet material, when first subjected to a heat-image and thereby provided with corresponding porous image areas 46, is found to be capable of causing image formation in a partially radiation-absorbent visibly heat-sensitive copysheet under brief intense irradiation as in thermographic back-printing procedures.

A typical illustrative process for making the sheet materials of the invention, illustrated schematically in FIG- URE 5, is as follows: a thin film 12 from stock roll is brought together with a porous paper web 13, from stock roll 51, at a knife coater comprising a bedplate 52 and knife 53. A dilute solution of adhesive is supplied from a feeder 54 to impregnate the Web 13. The composite next passes through an oven or drying duct 55 where the volatile solvent is removed, leaving the still porous web 13 adherently bonded to the film 12, forming at this point the simplified copy-sheet 46) of FIGURE 4. For the preferred form, however, the web is next coated with an adherent image-forming mixture, in this instance a fusible solid applied from a feeder 56 and maintained in liquid form by a heater 57, the liquid being spread by coating knife 58 operating in conjunction with bedplate 59. An impermeable film 14 from stock roll 60 is next applied at heated squeeze rolls 61, 62, the film being thus adherently bonded to the coated surface to form the finished copy-sheet product 11 which may then be wound into rolls, or cut into separate sheets, for example by shears 64.

The following specific examples will further illustrate the practice of the invention.

Example 1 Tensilized quarter-mil (.00025 inch) Mylar polyethylene terephthalate polyester film and thin porous tissue paper (7 /2 pound Super-Flexrope paper) are combined as shown in FIGURE 5 by impregnation with a solution in ethylene dichloride of a polymeric polyester of stoichiometric equivalents of polyethylene glycol and a mixture of equal weights of isophthalic and terephthalic acids. After drying, the still porous paper is next impregnated with a molten mixture of one part of Oil Black BT aniline dye in seven parts of Piccolastic thermoplastic resin melting at about 75 C., and the mixture is allowed to cool and solidify. A two mil (.002 inch) film of VBA 9925 vinyl chloride-vinyl acetate copolymer is then heat-pressed upon the resin-coated sheet to form a unitary three-layer composite which may be handled, rubbed against white paper, and otherwise manipulated as in the preparation of copies without transfor of color or delamination of the sheet.

The sheet is placed with the Mylar surface in contact with a portion of a printed page, such as a newspaper, which is then briefly exposed to intense radiation through the copy-sheet as in thermographic front-printing.

The sheet is next placed with the Mylar surface in contact with a sheet of white paper and is heated from the reverse surface by contact with a clean metal platen at 120 C. A copy of the printed original is obtained in the form of black images on the white paper background. Additional copies are obtained by heating the sheet material in contact with additional sheets of white paper. The metal platen remains clean-surfaced.

Example 2 A mixture of one part cetyl alcohol, two parts hexanediol, and one-half part of Crystal Violet 6B replaces the mixture of dye and resin employed in Example 1. The resulting sheet material produces brilliant blue image areas on the white paper by the copying procedures of Example 1 with the platen temperature at about 65 C. Effective copies on white fabric as well as paper receptor sheets may also be produced by subjecting the composite to brief intense irradiation as in thermographic backprinting.

Example 3 A mixture of seven parts Piccolastic resin and one part of behenoyl pyrogallate replaces the mixture of dye and resin employed in Example 1. The sheet material is substantially colorless. After front-printing against a printed original, the sheet is placed against a receptor sheet having a thin surface coating of silver behenate and resinous binder on white paper, and heat and pressure are applied with a smooth metal platen heated to about 275 F. A copy is obtained having black infra-red-absorbent image areas on a white reflective background.

With the platen at somewhat lower temperatures, no image is immediately observed on the treated receptor sheet; but subsequent heating of the receptor sheet to about 275 F. causes the development of the black image areas.

Example 4 Paper in contact with thin film as in Example 1 is first impregnated with a solution of 10 parts of polyester resin and 26 parts of methyl gallate in parts of tetrahydrofurane. Piccolastic resin is then added in molten form, followed by a 2-mil vinyl resin film as in Example 1. The sheet material is substantially colorless. Under the procedures and with the receptor sheets described in Example 3 and with the platen at C. there are produced a number of copies having sharply defined brownish-black images on opaque white backgrounds.

Similar results are obtained by coating the solution of methyl gallate and resinous binder directly on the thin polyester film and heat-sealing the vinyl resin film directly to the residual somewhat porous dried coating. The resulting sheet material is comparatively thin and flimsy, and has a tendency to wrinkle during handling and when locally heated, but produces equally sharp images on the treated receptor sheet when substituted for the sheet having the fibrous inner layer.

Example 5 To a concentrated dye solution prepared by acetone extraction of Plasto Violet MB organic dye is added a quantity of Lemac 1000 polyvinyl acetate resin. The solution is used to impregnate and unify the paper and to bond thereto the polyester and vinyl resin films as used in Example 1. The dark violet sheet material thus produced provides blue image areas on white paper when employed as described in Example 1 and with the platen at C., at which temperature the dye used is readily volatile. With substitution of Nacelin Black NR for the Plasto Violet MB and with a platen temperature of 150 C., brownish-black images are produced on white paper receptor sheets. Copies having improved appearance and permanence are prepared by substituting for the paper receptor sheet a treated paper having a surface coating of a mixture of 15 parts of polyester resin and 20 parts of precipitated calcium carbonate in parts of ethylene dichloride, and by subjecting the composite to brief intense radiation under thermographic backprinting procedures rather than heating with the heated platen.

Example 6 The sheet material prepared and thermographically processed as described in Example 1 is briefly pressed against a paper receptor sheet which has first been swabbed with heptane. A blue-black image is obtained. The process is repeated for a large number of copies.

Similarly, the processed sheet material of Example 2 provides a large number of copies when briefly pressed against paper receptor sheets moistened with methanol, i.e. by the spirit duplicator process.

In a similar process, using the processed sheet material of Example 4 with the silver behenate coated receptor sheet of Example 3, the latter being first swabbed with methanol, a visible copy is obtained only after heating the treated receptor.

Example 7 A partially processed sheet material prepared by combining the Mylar film and tissue paper as described in Example 1, and after drying but before application of the molten mixture of resin and dye, is combined with the vinyl copolymer film under heat and pressure. The resulting three-layer sheet material is placed with the polyester film surface against a printed original and the composite is briefly intensely irradiated by thermographic front-printing procedures. The processed sheet material is then placed with the perforate polyester film against a visibly heat-sensitive copy-sheet having a surface layer containing silver behenate and protocatechuic acid or other equivalent phenolic reducing agent in physically distinct and chemically inter-reactive relationship in ethyl cellulose or other film-forming binder, and the new composite is similarly irradiated. A copy is produced having brownish-black image areas corresponding to the printed original. A similar effect is obtained using the partially processed combination of Mylar film bonded to porous paper in the absence of the vinyl copolymer surface film.

The foregoing illustrative examples employ materials and components which have been found to provide useful results but the practice of the invention is not restricted thereto, as will appear from the following further illustrations.

One-half mil tensilized polypropylene film has proved a useful replacement for the one-quarter mil Mylar polyester film; since it is a somewhat softer film and shows a tendency toward tackiness when heated, it is found desirable to apply a minimal sizing coat, for example of dimethyl silicone fluid, over the exposed surface of the film before subjecting the sheet to a heat-image. Silicone fluid is also advantageously applied to the Mylar polyester film of Example 1 when the same is used in making copies of graphic intelligence printed with inks containing thermoplastic resin components. Polystyrene film of 1 /2 mil thickness has also been used.

Similarly, one mil polyvinyl fluoride film has been substituted for the two mil vinyl copolymer outer film layer. The thinner film produces a less bulky final product and increases the heat-resistance of the outer surface, an important consideration when using a heated platen or the like for transfer of image-forming components. Resistance to solvents is also markedly improved. The polyvinyl fluoride film is conveniently bonded to the surface of the impregnated paper by an intervening primer coating of thermoplastic vinyl acetate polymer applied from solution to the film and hot pressed against the paper layer.

Transparent films of regenerated cellulose (Cellophane) are useful as the outer film layer, particularly where thermographic means are employed in preparing the intermediate copy; thin opaque aluminum or other metal foil may be used where the heat-image is supplied from heated type faces. These and other analogous permanently impermeable pre-formed membranes or films are, like the polyvinyl fluoride film, particularly resistant to heat and solvents.

Various volatile reactant materials may replace the methyl gallate of Example 4 or the behenoyl py'rogallate of Example 3, depending on the nature of the co-reactant contained in the receptor sheet. 1-hydroxy-4-methoxynaphthalene is particularly effective in conjunction with noble metal salts such as silver behenate, and is also useful with iron salts, for example ferric stearate. Large numbers of volatile dyes may be used in place of those specified in Example 5, with transfer temperatures extending from as low as about C. to well above 200 C. Dyes such as Auramine Base, Autol Brilliant Red BND, Acetamine Scarlet B, Oil Blue A, Sudan Dark Brown BG Ex, and Alizarine are representative.

What is claimed is as follows:

1. A self-supporting unitary heat-sensitive sheet material suitable for image transfer from a graphic original to a receptor sheet by thermal procedures as herein described, said sheet material comprising a thin tensilized continuous thermoplastic film, another continuous film, and, between said films and adherently bonded thereto, a thin layer of a porous web containing an image-forming transfer material.

2. The sheet material of claim 1 in which the thermoplastic film has on the exterior surface thereof an extremely thin protective lubricant layer.

3. A self-supporting heat-sensitive sheet material com prising a thin tensilized continuous thermoplastic film, another continuous film, and a unified porous layer between and adherently bonded to said films; said thermoplastic film, on application thereto of a localized heatpattern, being rendered porous at heated areas.

4. A unitary heat-sensitive sheet material comprising in order a thin tensilized continuous thermoplastic film, a thin porous fibrous web, and permanently impermeable continuous film, said fibrous web being unified with a polymeric binder and containing an image-forming transfer material.

5. A unitary heat-sensitive sheet material comprising in order a thin tensilized continuous thermoplastic film, a thin porous paper, and a permanently impermeable continuous film, said paper being unified and adherently bonded to said films with a polymeric binder and containing an image-forming transfer material.

6. The sheet material of claim 5 in which the transfer material is a solid melting within the approximate range of 60-150 C.

7. The sheet material of claim 6 in which the transfer material is a colored wax-like solid.

8. The sheet material of claim 5 in which the transfer material is volatile within the approximate range of 60- C.

9. The sheet material of claim 8 in which the volatile transfer material comprises an organic dye.

1 0. The sheet material of claim 5 in which the transfer material is a co-reactant visibly inter-reactive with a reactant component of a receptor sheet.

11. The sheet material'of claim 10 in which the coreactant is a phenol.

12. The sheet material of claim 11 in which the phenol is volatile within the approximate range of 60150 C.

References Cited in the file of this patent UNITED STATES PATENTS 798,528 Ostwald Aug. 29, 1905 1,354,478 Gestetner Oct. 5, 1920 1,421,884 Yohns July 4, 1922 1,489,706 Loebcke Apr. 8, 1924 2,581,153 Wallich Jan. 1, 1952 2,651,255 Wallich Sept. 8, 1953 2,726,979 Grant Dec. 13, 1955 2,740,896 Miller Apr. 3, 1956 2,808,777 Roshkind Oct. 8, 1957 2,919,349 Kuhrmeyer Dec. 29, 1959 3,020,836 Palmer Feb. 13, 1962 

1. A SELF-SUPPORTING UNITARY HEAT-SENSITIVE SHEET MATERIAL SUITABLE FOR IMAGE TRANSFER FROM A GRAPHIC ORIGINAL TO A RECEPTOR SHEET BY THERMAL PROCEDURES AS HEREIN DESCRIBED, SAID SHEET MATERIAL COMPRISING A THIN TENSILIZED CONTINUOUS THEREMOPLASTIC FILM, ANOTHER CONTINUOUS FILM, AND, BETWEEN SAID FILMS AND ADHERENTLY BONDED THERETO, A THIN LAYER OF A POROUS WEB CONTAINING AN IMAGE-FORMING TRANSFER MATERIAL. 